Method and apparatus for centralized thermal recovery based on an oil reservoir by electric heating edge and bottom water layers with horizontal wells

ABSTRACT

A method for centralized thermal recovery, comprising: first, providing a horizontal well in the upper part of the water layer in which a heating system is configured; then centralized preheating the oil reservoir via electrically heating the water layer, then starting centralized producing the oil after the top of the oil layer reaches an expected temperature. An electric heating system for horizontal well to heat the water, comprising, an inner liner with the upper half slotted, a heat insulation board, a sealing board, a vacuum chamber, an electric heater, a ferrite permanent magnet rod.

RELATED APPLICATION

This application is a Continuation application of U.S. patent application Ser. No. 16/378,613, filed on Apr. 9, 2019, now abandoned which Claims priority to CN 201310689685.0 filed Dec. 12, 2013, all of which are hereby incorporated herein in their entireties by reference.

FIELD OF THE INVENTION

The present invention is suitable for oil and gas reservoirs with a water layer, such as heavy oil reservoirs and high pour-point oil reservoirs, which can be thermally recovered.

BACKGROUND OF THE INVENTION

Huff and puff or steam stimulation, steam flooding, hot-water flooding and in-situ combustion are all efficient technical methods in thermal recovery. However, with gradually in-depth development, more and more problems have been exposed in production. Especially for middle-deep to super-deep reservoirs (depth of 600˜2300 m), the contradiction in production is more prominent: 1) As pipeline and wellbore heat loss in steam huff and puff, steam drive, hot water drive is serious, thermal efficiency is low, the water production rate of production wells is high, the production rate is low, the decline rate is high, the ultimate recovery degree of the reservoir is affected; 2) although in-situ combustion is effective to production test of some common-heavy oil fault blocks and can satisfy the requirement of industrial production, it cannot be applied to most of the super-heavy oil reservoirs, in addition, the method is destructive to the reservoir. Once the reservoir is destroyed, any advanced thermal recovery method invented in the future will be impossible for operation; 3) the electric heating method is currently confined to the sucker rod and wellbore heating method. Its purpose is to improve the oil and gas lifting ability capacity of the production wells and to reduce oil viscosity and wax deposition of crude oil around the production wells; 4) horizontal well hydraulic fracturing and electric heating oil shale in-situ thermal recovery method is difficult to implement in heavy oil reservoirs, high cost and serious environmental pollution; 5) at present, all thermal recovery methods belong to a method of local heating oil layers. Oil layers are heated unevenly, the thermal holding time is short, the efficiency is low, and the remaining oil has high oil saturation, which is mainly concentrated in areas with low thermal energy and low thermal efficiency.

SUMMARY OF THE INVENTION

A trap is a place where oil and gas can continue to migrate and gather in it. The trap consists of three parts: reservoir, caprock and barrier which prevents oil and gas from migrating and causes oil and gas accumulation. It can be the bending deformation of cap rock itself, such as anticline, or other barriers, such as fault, lithological change, etc. In a word, the trap is an effective space for capturing dispersed hydrocarbons and has the ability to store oil and gas. Once an amount of oil and gas enters the trap, fills the trap or occupies a part of the trap, an oil and gas reservoir is formed. Any oil and gas reservoir with formation water can be treated as a whole sealed by cap rocks and barriers, including anticline structure, fault, lithological change, edge, and bottom water, etc.

A method for centralized thermal recovery of oil comprising, taking an entire oil reservoir in a trap as a whole to recover; providing at least one horizontal well in the top of the edge and bottom water layers, below the oil-water interface, and near the oil layers, with a heating system positioned in each horizontal well; centralized heating the edge and bottom water until the temperature of the whole oil reservoir rises to the state that the crude oil in place becomes moveable and recoverable; then stopping heating, and starting to centralized produce the crude oil with production wells. After the primary oil recovery, separating the residual oil and water in the reservoir by gravity and reheating the formation water for secondary oil recovery.

According to the method of centralized thermal recovery of oil, side-drill the horizontal well from an old well, or drill the horizontal well that meets the water layer directly.

According to the method of centralized thermal recovery of oil, drill a single horizontal well or multi-branch horizontal wells to heat the water. The horizontal wells are equably arranged in a plane in the top water layer. Determine the depth position of the horizontal section of the horizontal well based on the oil reservoir volume, and complete the horizontal well with gravel open-hole.

According to the method of centralized thermal recovery of oil, centralized recovering the mobilized oil with at least one production well, which are either vertical wells or horizontal wells, or any combination of these wells.

According to the method of centralized thermal recovery of oil, at first, electrically heat the water at high-power, and then reduce power to heat water comprising keeping the temperature of the horizontal well lower than Curie temperature.

Continuously electrically heat the water at a pressure lower than the reservoir fracture pressure. The temperature of the top oil reservoir rises up to at least viscosity-temperature inflection point, usually within the range of 80° C.˜150° C.

The reservoir pressure and temperature can be released with some production wells to prevent reservoir formation from cracking.

The feasibility of this centralized thermal recovery method is manifested in the following aspects: first, as the movement direction of heated water is upward, and the velocity of heat conduction of reservoir is higher than that of surrounding rocks, heat energy accumulates in the oil reservoir overtime.

Second, most of the reservoirs develop an edge and bottom water and contain adequate formation water resources, which make it possible that continuous electric-heating edge and bottom water is able to supply enough thermal energy to the oil reservoir.

Third, the formation water plays key roles during centralized thermal recovery at many aspects, such as the following:

-   -   the edge and bottom water plays a role of the heat transfer         medium;     -   the edge and bottom water plays a role of a coolant of the         immersion heaters;     -   the edge and bottom water plays a role of keeping petrophysical         characteristics of the reservoir from damage for the reason that         its salinity is similar to that of pore water in the oil         reservoir;     -   the edge and bottom water keep crude oil from heat damage         because the temperature of the preheated water is relatively         low;     -   the edge and bottom water storages enough heat and reduces         reservoir heat loss during centralized oil production;     -   the edge and bottom water is a material source of steam flooding         in the process of centralized oil production;     -   the edge and bottom water coning is a resource of hot water         driving energy in the process of centralized oil production         because of the strong fluidity and high thermal conductivity of         water, it can decrease the well pattern density of electric         heating horizontal wells;     -   the edge and bottom water flowing up and down is treated as a         source of induced heat provided the electric immersion heater         passes current which causes induced current in water due to its         electrical conductivity;     -   Influenced by geothermal gradient, the deeper the formation         water is buried, the higher the formation water temperature is,         and the more energy-saving electric heating the edge and bottom         water is;     -   because of the direction of heat transferring mainly upward, the         gravity differentiation of hot and cold water, as well as the         fact that thermal conductivity of surrounding rock is worse than         that of the reservoir, the thermal energy in edge and bottom         water mainly transfers upward with less heat loss and most         accumulates in the oil reservoir and the edge bottom water layer         above the plane of the horizontal well;     -   edge and bottom water resources are abundant and environmentally         friendly. Therefore the method of electric heating edge and         bottom water can be recycled.

A horizontal well electric heating system comprising an inner liner wherein the upper half of the inner liner slotted; a heat insulation board; a ferrite permanent magnet rod; an electric immersion heater; a vacuum-sealed chamber; and a sealing board.

The inner liner is configured to support the ferrite permanent magnet rod, the electric heater and the heat insulation board;

-   -   the upper half of the inner liner slotted allows formation water         and heat to flow freely;     -   the heat insulation board set at the diameter of the inner liner         is configured to prevent thermal energy loss from downward         transfer;     -   the ferrite permanent magnet rod fixed on the inner of the upper         half inner liner is configured to prevent scale;     -   the electric heater connected in series is waterproof and         spiral, provided on the heat insulation board, in the middle of         the upper inner liner is configured to generate resistant heat;     -   the vacuum sealed chamber enclosed by the sealing board, the         heat insulation board and the lower half of the inner liner is         configured to prevent thermal energy from transferring         downwards;     -   the sealing board set at two sides of the lower half of the         inner liner is configured to keep the inner liner stable;     -   the sealing board is configured to be made of a high-density         insulation plate, such as a lead plate, or other more effective         materials;     -   the insulation board is configured to be level and the slotted         upper inner liner is configured to be on the top.

The structure of the horizontal well electric-heater is shown in FIG. 1˜FIG. 1(c). The slotted inner liner 1 of horizontal-well 11 is divided into the two parts by a heat insulation board 4. The upper part is slotted, in which several spiral electric heaters 3 connected in series are set on the board which is set at the horizontal diameter of the inner liner. In the lower part, a vacuum chamber is enclosed by the lower inner liner, the sealing board 5 and the insulation board to prevent heat loss from downward transfer.

A connector system connects the electric immersion heater to an electric cable and a surface power unit, and delivers electric power to the electric heater through the electric cable.

The electric heating system preferably includes a thermocouple operatively connected to the surface power unit for monitoring heating time and heating temperature, accordingly, further to control the pressure of the oil reservoir according to the congruent relationship between boiling point and pressure of water.

Thermal energy comes from resistance heat generated by the electric heater and electromagnetic induction heat generated by upward moving formation water passing through electromagnetic field.

In another embodiment, a method of centralized thermal recovery comprising continuously centralized electrically heating the edge and bottom water at a temperature of the edge and bottom water around the immersion heater lower than 450° C.

The scale removal technology of magnet in electric heating effectively solves the scale phenomenon in the process of electric heating. Scale originates from the hard water quality. Magnets can soften water, which is environmental friendly, economical, convenient and safe. Ferrite permanent magnet, whose components mainly include BaFe12019 and SrFe12019, is made by ceramic technology, bears the characteristics of well temperature resistance, moderate price, and wide application. It is a preferred material for scale removal adapted to the environment of electric heating edge and bottom water layers.

Several ferrite permanent magnet rods are fixed on the inner of the upper slotted liner to prevent scaling. Magnetized water scale prevention principle is cited as follows:

The scale formed by water on the wall of the heater tube is hard to scale CaCO₃, which is called calcite. Its physical and chemical properties are similar to those of marble, with the compact arrangement and hard structure.

After magnetic treatment, the particle group of water becomes smaller, the conductance increases and the activity increases. When heated, impurities in water create a thin layer of soft dirt on the wall of the metal tube. It is characterized by the loose arrangement of molecules, disorder, poor adhesion to the metal pipe wall and easy to fall off. It can be reduced and eliminated by using a reliable magnetizer for a long time which has the function of differentiating and eliminating scale on existing scale devices.

The magnetizer can be divided into active and passive. Active is the electromagnet, which needs power and can control the magnetization. The passive source is made of the permanent magnet, which is connected to the water pipe. The water can be magnetized at any time without a power supply.

Curie temperature refers to the temperature at which a material can change between a ferromagnet and a paramagnet. When it is below Curie temperature, the material becomes a ferromagnet, and the magnetic field associated with the material is difficult to change. When the temperature is higher than Curie temperature, the material becomes a paramagnet, and the magnetic field of the magnets can easily change with the change of the surrounding magnetic field. It is reported that the Curie temperature of ferrite is about 450 degrees, usually greater than or equal to 450 degrees.

Beneficial Effect of the Invention

This is a centralized thermal recovery method based on an oil reservoir unit, i.e., unified heating and unified oil recovery for the whole reservoir, reflecting the scale effect of the whole reservoir preheating and centralized construction operation. It is different from the conventional thermal recovery method in which oil is produced while heating oil layers directly in a single well or group of wells. At the same time, it is also a kind of thermal recovery method which makes full use of natural formation water resources and their attributes and heats the whole oil reservoir by electric heating of formation water in horizontal wells. It can achieve the following beneficial effects: 1) The electric heating of formation water in horizontal wells is environmentally friendly, energy-saving, convenient, fast and easy to operate; 2) Thermal energy can be transmitted to reservoirs through water layers. Adequate heat can meet the needs of thermal recovery development, to solve the problems of reservoir thermal energy injection, small heating radius and short duration of thermal energy; 3) No use of surface water resources, no steam injection and sewage treatment processes, cost reduction, energy saving and environmental protection; 4) Reservoir in-situ thermal recovery method, no pipeline and wellbore thermal loss, thermal efficiency high, can effectively develop from deep to ultra-deep thermal recovery reserves; 5) High bottom water temperature, the whole reservoir crude oil in movable temperature conditions, combined with other driving energy, bottom water coning in the process of oil recovery can effectively form bottom water hot water flooding; 6) Unlimited requirements for reservoir geological characteristics, widely used in various oil reservoirs with edge and bottom water; 7) No damage to the reservoir and multiple recovery. The centralized thermal recovery method based on an oil reservoir by horizontal wells electric heating edge and bottom water layers has natural advantages, which can effectively solve many technical problems faced by conventional thermal recovery methods at present, and improve the production degree and ultimate recovery degree of reservoir reserves; 8) This method can be widely applied in thermal recovery of other similar types of mineral resources.

Meanwhile, multiple oil recovery mechanisms work well in centralized oil producing, including:

the thermal expansion pressure from water formations and oil layers;

the effect of synthesis steam flooding produced by water-soluble gas overflow, steam coming from the edge and bottom water as well as pore water, and pyrolysis gas from crude oil in bottom oil reservoirs;

hot water flooding due to edge and bottom hot water coning;

the viscosity-reduction effect/wax-precipitation effect of in-place oil under high temperature;

gravity drainage of the heated crude oil;

gravity differentiation among fluids after primary-centralized thermal recovery of oil for other times, and

combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a structure of an electric heating system positioned in a horizontal well.

FIG. 1a is a schematic diagram of the longitudinal profile of an electric heating system positioned in a horizontal well.

FIG. 1b is a schematic diagram of the cross section of an electric heating system positioned in a horizontal well.

FIG. 1c is a side view of the line of an electric heating system positioned in a horizontal well.

FIG. 2 is a schematic diagram of wellbore structure of an electric heating horizontal well for centralized thermal recovery method based on an oil reservoir by electric heating edge and bottom water layers with horizontal wells.

FIG. 3 is a schematic diagram of horizontal heating well for centralized thermal recovery.

FIG. 4 is a schematic diagram of heat transfer direction of electric heating system in horizontal wells

The solid arrow indicates the direction of direct radiant heat energy from the electric heater, and the dotted arrow indicates the direction of heat energy transfer after being reflected by the heat insulation board.

FIG. 5 is a schematic diagram of temperature distribution curves in oil reservoir under 15 MPa pressure during centralized thermal recovery by numerical simulation. E1 and E2 respectively represent Profile Temperature of Electrically Heated Horizontal wells, and

P stands for Inter-well profile temperature of electric-heating horizontal wells, and the shaded area is the vaporized area when the bottom water invades under the condition of 15 MPa.

DETAILED DESCRIPTION

Label 1 in each figure refers to a slotted upper inner liner. Its function mainly has two points: one is to suspend the permanent magnet rods to protect the electric heater from the pressure of the upper stratum; the other is to allow the formation water to enter and leave the slotted screen pipe freely, so that the water and the electric heater can fully contact, so as to better play the thermal conductivity of water.

Label 2 refers to ferrite permanent magnet rods used to prevent scaling. According to FIG. 5 the prediction diagram of the relationship between water boiling point temperature and pressure, the higher the formation pressure is, the higher the water boiling point temperature is, and the corresponding fitting mathematical relationship is as follows:

Y=178.27x ^(0.2509)

-   -   Note: y: Boiling point temperature; x: pressure MPa.         Under the condition of electrically heated formation water, the         boiling point temperature corresponding to formation water under         15 MPa is predicted to be 350 degrees Celsius and that         corresponding to 28 MPa is about 450 degrees Celsius. Therefore,         as long as formation pressure and the boiling point temperature         of formation water are controlled to be lower than the Curie         temperature 450 degrees Celsius of ferrite permanent magnet, the         magnetism of permanent magnet will not be destroyed. At the same         time, it must be noted that when the electric heater is DC, the         magnetic pole of the ferrite permanent magnet rod must be in the         same direction as the electromagnetic field produced by the         electric heater. Otherwise, the magnetic force of the permanent         ferrite magnet rod will gradually weaken.

Label 3 refers to a waterproof spiral electric heater connected in series. The electric heater is connected to the ground power supply through a coaxial cable. When current is applied, the spiral electric heater will generate resistance heat to heat the edge and bottom water directly, the heated edge and bottom water will transfer mainly upwards and cold water will move downwards, which makes the surrounding water moving up and down produce electromagnetic induction heat. During this period, when the direction of the magnetic field is the same as that of the electromagnetic field, the ferrite permanent magnet rods will enhance the intensity of the electromagnetic field produced by the electric heater, and vice versa, weaken the induction phenomenon of the electromagnetic field.

Label 4 refers to the heat insulation board. As shown in FIG. 4, the heat energy from the electric heater radiates to the surrounding area, and the upward heat is transferred with the upward movement of formation water, while the downward heat energy is reflected by the insulation plate, and only a very small amount of heat energy is transmitted downward. Another function of the heat insulation board 4 is to sustain the waterproof spiral electric heater connected in series 3.

Label 5 refers to a sealing board. Label 15 indicates the sealed vacuum chamber enclosed by the heat insulation board, the sealing board and the lower half of the inner liner. It keeps heat from transferring downward together with the heat insulation board.

Label 6 in FIG. 2 refers to the water and oil interface. The electric heating system is configured to be positioned in a horizontal well filled with gravel for open hole completion, as label 8. Label 7 refers to reservoir top interface, and labels 6 to 7 are reservoir thickness. Label 9 refers to a coaxial cable connecting the power supply and electric heater. Closed waterproof treatment is needed at the joint of the coaxial cable and electric heating system. Label 10 refers to a power supply, provided either a DC or AC. Label 11 in FIG. 2 and FIG. 3 refers to a single electric heating horizontal well extending in edge and bottom water layers.

Label 12 in FIG. 3 refers to an oil reservoir, label 13 refers to the edge and bottom water layers, at least one or more single electric heating horizontal wells are provided in at least one or more edge and bottom water layers on a horizontal plane 14 below oil-water interface 6. The single horizontal wells can be substituted by branched electric heating horizontal wells in order to increase electric heating efficiency and reduce the operating cost of single horizontal wells.

FIG. 5 shows that as the boiling point temperature of water corresponding to the formation pressure of 15 MPa is 350 degrees Celsius, the shaded area is the vaporized area when the bottom water invades under the condition of 15 MPa. FIG. 5 also shows that some of the formation crude oil will be pyrolyzed, resulting in a small amount of pyrolytic gas. These factors are conducive to improving the efficiency of centralized oil recovery. When the electric heating stops and enters the production stage, the temperature inside the reservoir will drop below the boiling point temperature of water step by step, and the generation of this part of water vapor and pyrolysis gas will end.

Example

A numerical simulation result shows that the static pressure in the reservoir quickly changes to thermal expansion pressure after electric heating edge and bottom water layer, and the pressure distribution is relatively uniform, which corresponds to the boiling point temperature of formation water one by one. When the electric heating stops and enters the production stage, the reservoir enters the step-down production stage, and the pressure drop is relatively fast until the end of production, and the pressure drops to 2 MPa. Obviously, the magnitude of thermal expansion pressure plays an important role in the process of oil recovery.

The temperature distribution curves in oil reservoir during centralized thermal recovery shows that the characteristics of temperature is different from that of the pressure distribution, the temperature in the oil reservoir undergoes a gradual accumulation process during the centralized electric heating process. The temperature at the bottom of the reservoir is obviously higher than that at the top, and the temperature above the electric heating horizontal well is higher than that between wells. When the electric heating is stopped, the well closure is conducive to the further uniform diffusion of unbalanced heat in the oil reservoir. In the stage of centralized production, the reservoir temperature gradually decreases with the production of crude oil and becomes more uniform. Due to the thermal insulation of the formation water, the reservoir temperature remained at a high level of about 180 degrees Celsius until the end of production.

FIG. 5 is a schematic diagram of temperature distribution curves in oil reservoir under 15 MPa pressure at the time of stopping electric heating by numerical simulation. The boiling point temperature of water corresponding to the formation pressure of 15 MPa is 350 degrees Celsius, that is to say, in the oblique shaded part of the figure, wherein the temperature is up to 650 degrees Celsius which is much higher than 350 degrees Celsius, pore water in the oil reservoir exists in a vapor state. At the same time, some of the formation crude oil will be pyrolyzed, resulting in a small amount of pyrolytic gas. These factors are conducive to improving the efficiency of centralized oil recovery. When the electric heating stops and enters the production stage, the temperature inside the reservoir will drop below the boiling point temperature of water step by step, and the generation of this part of water vapor and pyrolysis gas will end.

After centralized electrically heating the bottom water for 1100 days, the top temperature of the reservoir reaches 150 degrees Celsius. The production peak period produces 65-90 t/d of oil per day, the stable production time is 1405 days, and the recovery degree of primary production is as high as 53.8%.

Another example of centralized electric heating the bottom water for 730 days, the top temperature of the reservoir reaches 80 degrees Celsius. The stable production time is 1249 days, and the recovery degree of primary production is as high as 34.5%.

INDUSTRIAL APPLICABILITY

the method and the electric-heating system are applied to thermally recover heavy oil reservoirs and high pour-point oil reservoirs with edge and bottom water layers, especially for those oil reservoirs in the depth of middle-super deep depth which are difficultly recovered, and are widely adapted to thermal recovery of other similar types of mineral resources. 

1. A method for centralized thermal recovering oil, for an oil reservoir with a water layer and an oil layer, comprising: providing a horizontal well in the upper part of the water layer, centralized preheating the oil reservoir via centralized heating the water layer, and starting centralized producing the oil after the top of the oil layer reaches an expected temperature.
 2. the method according to claim 1, wherein, comprising side-drilling the horizontal well from an old well extending into the top water layer, or drilling the horizontal well that meets the water layer directly.
 3. the method according to claim 2, wherein, comprising drilling multi-branch horizontal wells in the top water layer.
 4. the method according to claim 1, wherein, comprising arranging the horizontal wells in a plane in the water layer, and determining the depth position of the horizontal section of the horizontal well based on the oil reservoir volume, and completing the horizontal well with gravel open-hole.
 5. the method according to claim 1, wherein, comprising providing a heating system inside the horizontal well.
 6. the method according to claim 5, wherein, comprising providing an electric-heating system inside the horizontal well.
 7. the method according to claim 1, wherein, comprising centralized heating the overall oil reservoir in each individual trap when electrically heating the water layer.
 8. the method according to claim 1, wherein, comprising keeping the pressure of the oil reservoir lower than the fracture pressure of the reservoir when electrically heating the water layer.
 9. the method according to claim 1, wherein, comprising starting to electrically heat formation water at high-power, and then reducing power to heat water, comprising keeping the temperature of the horizontal well lower than Curie temperature.
 10. the method according to claim 8, 9, wherein, comprising decreasing the pressure or temperature of the oil reservoir to keep the pressure of the oil reservoir lower than the fracture pressure and the temperature lower than Curie temperature.
 11. the method according to claim 1, wherein, comprising stopping electrically heating after the centralized oil producing.
 12. the method according to claim 1, wherein, comprising: preheating the oil reservoir until the top oil becomes movable and recoverable.
 13. the method according to claim 1, wherein, comprising: after centralized producing the oil, separating the residual oil and the water by gravity differentiation, and reheating the water for secondary oil recovery.
 14. An electric-heating system for horizontal well, comprising, an inner liner having a cavity; a heat insulation board inserting into the cavity along the diameter of the inner liner; two sealing boards provided on each side of the lower liner; an electric heater provided on the heat insulation board in the middle of the upper cavity; and a ferrite permanent magnet rod fixed on the inner of the upper inner liner; wherein the lower half of the inner liner, the heat insulation board, and the sealing board form a vacuum chamber.
 15. the electric-heating system according to claim 13, wherein, the insulation board and the vacuum-enclosed chamber is configured to reduce downward transmission of thermal energy.
 16. the electric-heating system according to claim 13, wherein, the sealing board is configured to be made of a high density insulation plate.
 17. the electric-heating system according to claim 13, 15, comprising, the sealing boards provided on each side of the lower liner keep the inner liner stable; and the insulation board is configured to be level and the slotted upper inner liner is configured to be on the top.
 18. the electric-heating system according to claim 13, wherein, the slotted upper half of the inner liner is configured to allow water and heat to flow.
 19. the electric-heating system according to claim 13, comprising, the electric heater is configured to be waterproof, spiral, and in series connection, and to reduce the scale formation.
 20. the electric-heating system according to claim 13, wherein, the ferrite permanent magnet rod is configured to remove the scale.
 21. the electric-heating system according to claim 13, wherein, the insulation board and the vacuum chamber are configured to keep from the downward heat loss. 